1. Field of the Invention
The present invention relates to a radio paging receiver and, more particularly, a radio paging receiver for displaying/calling a message corresponding to message data in a radio signal which is transmitted from a base station of a radio paging system.
2. Description of the Prior Art
FIG. 17 is a block diagram showing a circuit configuration of a radio paging receiver in the prior art. In FIG. 17, a receiver portion 21 is a circuit which receives a radio signal transmitted from a base station of a radio paging system via an antenna 21a, and then demodulates the radio signal into a digital signal. A decoder 22 is a circuit which applies a bit synchronization process and an error correction process to the received signal being converted into the digital signal, and then collates an address in the received signal with own address loaded in a memory portion 23. The memory portion 23 is a memory unit which has a memory element for erasing and writing data electrically, e.g., EEPROM (Electrically Erasable Programmable Read Only Memory), etc., and stores own address of the radio paging receiver, etc. A CPU 24 is a CPU (Central Processing Unit) which controls peripheral circuits based on the received signal sent out from the decoder 22.
A display driver 25 is a circuit which drives a display portion 26 based on a display signal issued from the CPU 24. The display portion 26 is a unit which is driven by the display driver 25, and then displays data, etc. by liquid crystal elements, etc. in response to the display signal. A switch portion 27 is a unit which generates instructions according to the user's operation and various data. A signal issued from the switch portion 27 is input into the CPU 24 via the decoder 22. An informing driver 28 is a circuit which controls an informing portion 29 consisting of a speaker, a vibrator, etc.
Next, an operation of the above radio paging receiver will be explained hereunder. In the radio paging receiver, the receiver portion 21 receives the radio signal being transmitted from the base station (referred simply to as a “base station” hereinafter) of the radio paging system via the antenna 21a at a predetermined timing controlled by the CPU, then converts the radio signal into the digital signal by amplifying, frequency-converting, detecting and demodulating the received radio signal, and then sends out the digital signal to the decoder 22. The decoder 22 applies the bit synchronization process and the error correction process to the digital signal supplied from the receiver portion 21, and then collates an address contained in the received signal with own address read from the memory portion 23 via the CPU 24 to confirm whether or not the received signal is directed to own radio paging receiver.
If the received signal is directed to own radio paging receiver and message data is contained in the received signal, the decoder 22 picks up the message data, and then sends out the message data to the CPU 24 and also outputs a driving signal to the informing driver 28. In parallel with this calling operation, the CPU 24 converts the message data into the display signal which consists of a combination of bit codes each having the predetermined bit number, and then sends out the display signal to the display driver 25. The display driver 25 drives the display portion 26 based on the display signal sent out from the CPU 24 to display the message corresponding to the message data on the display portion 26. After the calling operation has been completed, the CPU 24 stores the message data in a RAM 24a. 
In this manner, in the prior art, the radio paging receiver receives the radio signal sent out from the base station, then executes the calling operation by a ringer tone, etc. and displays the message contained in the radio signal, and then stores the message data in a RAM.
However, according to the above radio paging receiver, when the message data cannot be stored in a storage area, they are erased automatically in the order of older receiving time or they are erased from the storage area separately or collectively according to the user's operation. In addition, in case an information broadcasting service is carried out by using the radio paging receiver, various information such as daily divination, sports prompt report, weather forecast, etc., which are available only on a certain day, are stored in the message storage area.
Accordingly, according to the radio paging receiver in the prior art, the user must erase the stale information from the storage area each time. As a result, the radio paging receiver has such a problem that its utilization has become troublesome because of the frequent user's operation of erasing the message data, and thus the storage area has not been able to be utilized effectively.